Polarized and nonpolarized dermoscopy - The explanation for the observed differences
Memorial Sloan-Kettering Cancer Center, New York, New York, USA.Archives of dermatology (Impact Factor: 4.79). 07/2008; 144(6):828-9. DOI: 10.1001/archderm.144.6.828
Differences in observed structures, colors, and patterns present in lesions imaged with nonpolarized dermoscopes (NPDs) and polarized dermoscopes (PDs) have been previously noted.1- 2 Herein we address the science behind the differences observed and present representative lesions in which these differences can be appreciated. Under normal conditions, most of the light that impinges on the skin surface will be reflected (ie, specular reflectance or glare) due to the higher refractive index of the stratum corneum (1.55) compared with that of air (1.0). An NPD reduces this reflection by using a liquid interface that optically matches the refractive index of the glass plate of the dermoscope (approximately 1.52) with the stratum corneum.1 Elimination of the air interface reduces the amount of light reflected off the stratum corneum (Figure 1, blue line) and allows for increased light penetration into the skin (Figure 1, red and black lines). Light that is being scattered from below the corneal layer (Figure 1, red dashed and black lines) allows for the direct observation of underlying dermoscopic structures. A PD reduces the visualization of surface-reflected light through the use of 2 polarizers with orthogonal axes (intersecting at 90°). Light passing through the source polarizer is unidirectional and will be rejected by the detector polarizer unless it changes its direction of polarization. Since polarized light reflected from the superficial layers of the skin (Figure 1, blue and red lines) maintains its original polarization, it is completely rejected by the detector polarizer. Polarized light scatters as it penetrates the skin and, on average, undergoes 10 scattering events before its polarization is randomized (Figure 1, black line).3- 4 The depth that polarized light penetrates before undergoing 10 scattering events is approximately 60 to 100 μm. In other words, most of the light returned is from deeper layers (Figure 1, black line) and not singly backscattered light (Figure 1, red line) or surface-reflected polarized light (Figure 1, blue line). These physics explain the differences between PD and NPD observations and account for the depth of the skin each device can visualize. An NPD is better able to visualize the superficial layers of the skin, thus allowing for the easy identification of structures such as milialike cysts and the blue-white veil associated with orthokeratosis (Figure 2A and C). In contrast, a PD is essentially “blind” to the superficial layer and thus will not allow the observer to appreciate these structures, which may be important diagnostic cues for some lesions such as seborrheic keratosis (Figure 2B and D). However, by eliminating the superficial glare, PD allows for better appreciation of deeper structures such as the vasculature and collagen (Figure 2D and F), which may be helpful in identifying some malignant neoplasms.1
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- "The most distinctive clincher for dermoscopic feature of psoriasis includes presence of perifollicular scales and red loops. Deeper vasculature structures are better visualized in the polarized light. Although red loops were not observed in our study, red dot was observed in 50% of patients [Figure 9]. "
ABSTRACT: Aims:The aim was to study the trichoscopy features of selected hair and scalp conditions by two dermoscopic devices with different modes that is, polarized (noncontact) and nonpolarized (contact) mode.Materials And Methods:The present study included 11 clinical varieties of cases with total 112 patients, attending Sir Takhtasinh Hospital, Bhavnagar in the last 2 years. The clinical history was recorded for each case, and images were taken in both the Heine and DermLite II pro dermatoscope. We used polarized mode of the noncontact device (DermLite II) and the nonpolarized mode of the contact device (Heine) for our study.Statistical Analysis Used:Fisher's exact test to study dermoscopic observations for each mode.Results:We observed different nonscarring alopecia cases such as alopecia areata, androgenetic alopecia, trichotillomania, and tinea capitis. Scarring alopecia included discoid lupus erythematosus, lichen planopilaris, pseudopelade of Brocq, systemic lupus erythematosus. Scaling disorders included the psoriasis and seborrheic dermatitis. Furthermore, infestations like pediculosis capitis were included in the study. Various features were divided into follicular, interfollicular, pigmentary, vascular and hair shaft patterns. Each of the features was correlated in both the Heine (nonpolarized) and DermLite II (polarized) dermoscope, and observational finding was put forward accordingly.Conclusions:Various variations were observed in the documentation of dermoscopic patterns of the two dermatoscopes with certain features such as vascular patterns, scaling, and reticular pigmentation being better appreciated in polarized mode, while certain features were better documented in nonpolarized mode that is, black dots and tapered hair.
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- "Dermatoscopy relies on either fluid immersion or cross-polarization to reduce light scatter at the air-skin interface, and it is known that these different methods have an impact on the colors and structures which are displayed . Non-polarized dermatoscopy has been said to provide superior rendition of superficial structures while polarized dermatoscopy reveals a clearer rendition of deeper structures as well as of structures not seen with non-polarized dermatoscopy, including four-dot clods (also known as rosettes) and polarizing-specific white lines (also known as chrysalis, crystalline structures and shiny white streaks) . "
ABSTRACT: We report a case of a melanoma arising in a congenital-type compound nevus, which was excised because it was observed by both the patient and the treating dermatologist to have changed. Because the lesion was routinely photo-documented with both polarized and non-polarized dermatoscopy images prior to excision, these images were available for subsequent examination. Matched images are presented in what appears to be unique in the published literature: polarizing-specific white lines are identified as a compelling clue to the diagnosis of melanoma in a lesion that contains no clues apparent in the non-polarized image. Dermatopathology images reveal that the melanoma is arising in conjunction with a congenital type nevus. As expected, dermatoscopic polarizing-specific white lines are evident on the melanoma but not the nevus, and while a possible explanation is discussed, this remains speculative.
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- "Dermoscopic criteria for melanocytic and nonmelanocytic lesions, as well as the ones leading to the diagnosis of benign or malignant lesions, have nowadays come straight in the daily clinical practice. Dermoscopy techniques are based on a light source, that may be polarized or non-polarized, giving rise to a coloured magnified image . The digitization techniques allowed to collect lesion images to be compared and to evaluate changes over time  . "
ABSTRACT: Nodular lesions can be difficult to diagnose under dermoscopy alone, since they often lack specific diagnostic features. Confocal microscopy can be used as an aid to dermoscopy, to increase the diagnostic accuracy on equivocal skin lesions. We report three cases of bluish nodular lesions, difficult to diagnose under dermoscopy alone. Confocal features were very useful in these cases to lead us to the correct diagnosis, recognizing benign versus malignant entities. Histopathology is also reported, with high correspondence compared to the confocal imaging.
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